radio: image alignment

Summary:
Make radio widget handle image alignment and checkbox/radio button
alignment nicely, round 2.

{F13203}

Test Plan: http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22Felipe%20has%20a%20piano%20lesson%20at%20%243%5C%5Ccolon30%24.%20%5Cn%5Cn%20**%20Which%20clocks%20read%20%243%5C%5Ccolon30%24%3F**%20%20%5Cn%5Cn%5B%5B%E2%98%83%20radio%201%5D%5D%5Cn%22%2C%22widgets%22%3A%7B%22radio%201%22%3A%7B%22type%22%3A%22radio%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22choices%22%3A%5B%7B%22correct%22%3Atrue%2C%22content%22%3A%22Some%20text%20!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F45b907a37f7e04ab9083dd556d969d952684c0ac.png)%20%24n%24%20%24y%24%22%7D%2C%7B%22correct%22%3Afalse%2C%22content%22%3A%22Wrapped%20text%2C%20lorem%20ipsum%20dolor%20sit%20amet%2C%20consectetur%20adipiscing%20elit.%20Maecenas%20at%20fringilla%20mi%2C%20nec%20luctus%20nibh.%20In%20convallis%20velit%20quis%20turpis%20suscipit%20semper.%20Sed%20nunc%20nisl%2C%20eleifend%20ut%20pulvinar%20at%2C%20viverra%20sed%20orci.%20Ut%20lorem%20velit%2C%20tempor%20in%20leo%20eu%2C%20posuere%20vehicula%20lacus.%22%7D%2C%7B%22correct%22%3Afalse%2C%22content%22%3A%22hi%20!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F532e37eabdefef392180ea641b6c6a8c25e59475.png)%20jhkhkhka%20d%20hafdsk%20fadkjdk%20fa%20dsfkka%20dkj%20adfska%20adsfk%20fka%20ak%20fka%20ada%20afsdk%20afdj%20dfask%20adfadfkjfad%20ad%20sdfjkfa%20afjfadkafdkaafd%20f%20afda%20afakjdfj%20af%20afd%20fdjka%20afdks%20k%22%7D%2C%7B%22correct%22%3Afalse%2C%22content%22%3A%22!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F2ef203520d67f533319ae07bc76499b6ff383489.png)%20%20%22%7D%2C%7B%22content%22%3A%22fdakhj%20afdjh%20fadsjk%20fdahkdf%20dfsakj%20dfaskjfds%20fkdashda%20kdfj%20fdakj%20fdskjafd%20kdfa%20adjkfdas%20afdkjh%20kjfadhadf%20kjfda%20fakjfdas%20fdkjfa%20kjfadf%20afjkad%20fdakjfd%20kfajd%20hk%22%2C%22correct%22%3Afalse%7D%5D%2C%22randomize%22%3Afalse%2C%22multipleSelect%22%3Atrue%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22Select%20all%20correct%20answers.%20%20%22%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22hints%22%3A%5B%7B%22content%22%3A%22An%20analog%20clock%20has%20the%20hour%20hand%20in%20between%20the%20hour%20%24%5C%5Cred%7B3%7D%24%20and%20%24%5C%5Cred%7B4%7D%24.%20%20The%20minute%20hand%20has%20passed%20%2430%24%20tick%20marks.%20%20%5Cn%5CnIt%20is%20%24%5C%5Cred%7B3%7D%5C%5Ccolon%5C%5Cblue%7B30%7D%24.%5Cn%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F63bad9a3e2af080db5be61880e55ff09af2bc477.png)%22%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22A%20digital%20clock%20has%20a%20%24%5C%5Cred%7B3%7D%24%20in%20the%20hour%20place%20and%20%24%5C%5Cblue%7B30%7D%24%20in%20the%20minute%20place.%20%5Cn%5Cn%20It%20is%20%24%5C%5Cred%7B3%7D%5C%5Ccolon%5C%5Cblue%7B30%7D%24.%20%20%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F09776cd1d8bcac81c62d2e33ea9d6d29190e5c13.png)%22%2C%22widgets%22%3A%7B%7D%7D%2C%7B%22content%22%3A%22These%20clocks%20show%20%24%5C%5Cred%7B3%7D%5C%5Ccolon%5C%5Cblue%7B30%7D%24.%5Cn%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F63bad9a3e2af080db5be61880e55ff09af2bc477.png)%5Cn%5Cn!%5B%5D(https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2F09776cd1d8bcac81c62d2e33ea9d6d29190e5c13.png)%22%2C%22widgets%22%3A%7B%7D%7D%5D%7D

Reviewers: alpert, alex

Reviewed By: alpert

CC: alpert, eater

Differential Revision: http://phabricator.khanacademy.org/D6791